how to check if a number is a number in c code example

Example 1: how to know if a number is even in c

if((x & 1) == 0)
    printf("EVEN!\n");
else
    printf("ODD!\n");

Example 2: c check if char is number

char c = 'a'; // or whatever

if (isalpha(c)) {
    puts("it's a letter");
} else if (isdigit(c)) {
    puts("it's a digit");
} else {
    puts("something else?");
}